If you’re preparing for a Java job interview, you’ve probably spent hours researching and studying the most common interview questions. But with so many resources available online, it can be overwhelming to sift through them all.
That’s where this list of 180 Core Java interview questions and answers comes in. In this comprehensive guide, we’ve compiled the most commonly asked and important Java interview questions that you need to know to ace your upcoming interview.
1. What is Java?
– Java is a high-level, object-oriented programming language developed by Sun Microsystems in the early 1990s. It is known for its platform independence, meaning that Java code can run on any device or operating system that has a Java Virtual Machine (JVM).
2. What are the main features of Java?
– Some of the key features of Java include:
– Object-oriented: Java is based on the concept of objects and classes.
– Platform-independent: Java code can run on any device or operating system.
– Simple and easy to learn: Java has a straightforward syntax that is easy for beginners to grasp.
– Secure: Java has built-in security features to protect against viruses and hacking.
– Robust: Java is designed to be reliable and error-free.
3. What is the difference between JDK, JRE, and JVM?
– JDK (Java Development Kit) is a software development kit that contains all the tools needed to develop, debug, and run Java applications.
– JRE (Java Runtime Environment) is a subset of the JDK that includes the necessary tools to run Java programs, but not to develop them.
– JVM (Java Virtual Machine) is an abstract machine that runs Java bytecode and converts it into machine code that can be executed by the underlying hardware.
4. What is the difference between abstract class and interface in Java?
– An abstract class is a class that cannot be instantiated and may contain both abstract and concrete methods. Interfaces, on the other hand, are collections of abstract methods that can be implemented by classes.
– In Java, a class can implement multiple interfaces, but can inherit from only one abstract class.
5. What is a constructor in Java?
– A constructor is a special method that is called when an object is created. It is used to initialize the object’s state and set its initial values.
6. What is the difference between compile-time and runtime polymorphism?
– Compile-time polymorphism, also known as method overloading, occurs when two or more methods in a class have the same name but different parameters. The correct method is determined at compile time based on the arguments passed to the method.
– Runtime polymorphism, also known as method overriding, occurs when a subclass provides a specific implementation of a method that is already defined in its superclass. The correct method is determined at runtime based on the object’s type.
7. What is garbage collection in Java?
– Garbage collection is the process of automatically reclaiming memory that is no longer being used by the program. In Java, the garbage collector runs in the background and periodically checks for objects that are no longer referenced by the program, freeing up memory for other objects.
8. What is the difference between equals() and == in Java?
– The equals() method is used to compare the values of two objects, while the == operator is used to compare the references of two objects. In other words, equals() compares the content of objects, while == compares their memory addresses.
9. What is the difference between StringBuffer and StringBuilder in Java?
– StringBuffer is a thread-safe class that is synchronized, while StringBuilder is not thread-safe. This means that using StringBuilder in a multi-threaded environment can lead to potential race conditions, while StringBuffer is safe to use in such scenarios.
10. What is the difference between checked and unchecked exceptions in Java?
– Checked exceptions are exceptions that are checked at compile time and must be handled using try-catch blocks or by declaring them in the method signature using the throws keyword. Unchecked exceptions, on the other hand, are exceptions that are not checked at compile time and do not have to be caught or declared.
These are just a few of the 180 Core Java interview questions and answers that you need to know to prepare for your Java job interview. By familiarizing yourself with these questions and practicing your answers, you’ll be well-equipped to impress your interviewer and land your dream job in Java development. Good luck!
